A number of resin components are utilized, for example, for image output equipment such as copying machines and printers, electric/electronic equipment such as home electric appliances and interior components in automobiles. For these resin components, flame retardancy is required of resin materials for fire spreading prevention purposes.
In particular, copying machines have in their interior a fixation unit that becomes an elevated temperature state, and resin materials are also used at portions around the fixation unit. Further, copying machines are provided with a unit for the generation of a high voltage such as an electrification unit and a 100-V alternating current power supply unit. These units have a maximum power consumption of several hundreds of watts to 500 watts and are constituted by units utilizing a power system of 100 V and 15 A.
Such copying machines, mainly multi-function copying machines typified by multi-function printers, are stationary electric/electronic equipment, and, in international standards regarding flame retardancy of resin materials (IEC60950) that are one of safety standards for product equipment, ignition sources or portions in danger of ignition are required to be covered by an enclosure component having a flame retardancy level of “5V” as specified in UL94 standards (Underwriters Laboratories Inc., standard). The testing method for “5V” in UL94 standards is defined as “A flame test by a 500-W testing flame” in international standards IEC60695-11-20 (ASTM D 5048).
For components for the construction of a copying machine body, interior components within the enclosure in addition to components for the enclosure are required to meet “V-2” or higher level in UL94 standards. The testing method for the “V-2” or higher level in UL94 standards is defined as “A 20-mm vertical flame test” in international standards IEC60695-11-10, method B (ASTM D 3801).
Flame retardants that can be added to the resin material are divided into several types, and those commonly used herein are bromine flame retardants, phosphorus flame retardants, nitrogen compound flame retardants, silicone flame retardants, and inorganic flame retardants. Flame retarding mechanisms of these flame retardants are already known in several documents, and three flame retarding mechanisms that are adopted particularly frequently will be described here.
The first flame retarding mechanism is one using halogen compounds typified by nitrogen flame retardants. For example, halogen compounds are allowed to act as a negative catalyst in an oxidation reaction on a combustion flame to lower a combustion speed.
The second flame retarding mechanism is one using phosphorus flame retardants or silicone flame retardants. Bleeding of silicone flame retardants on the surface of the resin during combustion or a dehydration reaction of phosphorus flame retardants within the resin results in the production of a carbide (char) on the surface of the resin to form a heat insulating film that stops burning.
The third flame retarding mechanism is one using inorganic flame retardants such as magnesium hydroxide or aluminum hydroxide.
The combustion is stopped, for example, by cooling the whole resin through the utilization of an endothermic reaction that takes place upon the decomposition of these compounds by the combustion of the resin, or an evaporative latent heat possessed by the produced water.
On the other hand, conventional resin materials are made of plastic materials using petroleum as a starting material. In recent years, however, attention has been drawn to biomass derived resins using, for example, plants as a starting material. The biomass resource means that organisms such as plants or animals are used as a resource. Examples of biomass resources include woods, corns, fats and oils obtained from soybeans or animals, and raw refuses. Biomass-derived resins are produced using these biomass resources as starting materials. Biodegradable resins are also generally known. Biodegradation refers to a function of being degraded by, for example, microorganisms under certain environments in terms of temperature and humidity.
Some biodegradable resins are resins that are not biomass-derived resins but petroleum-derived resins and are biodegradable.
Biomass-derived resins include poly lactic acid (PLA) produced by chemical polymerization using, as a monomer, lactic acid produced by fermenting saccharides such as potatoes, sugar canes, and corns, esterified starches composed mainly of starch, in microorganism-producing resins (poly hydoroxy alkanoate) that are polyesters, which microorganisms produce in their bodies, and PTT (poly trimethylene terephtalate) produced by a fermentation method using, as starting materials, 1,3-propanediol and petroleum-derived terephthalic acid.
At the present time, petroleum-derived starting materials are used. However, studies are advanced aiming at the transfer of resins produced using petroleum-derived starting materials adopted at the present time to biomass-derived resins in the future. For example, succinic acid that is one of main starting materials for PBS (poly butylene succinate) is produced using a plant-derived starting material. Among such biomass-derived resins, products produced by applying poly lactic acid that has a high melting point around 180° C., possesses excellent moldability, and can be stably supplied to the market are becoming realized.
The poly lactic acid, however, has a low glass transition point of 56° C. and, for this reason, has a low thermal deformation temperature around 55° C., indicating that the poly lactic acid has low heat resistance. In addition, since the poly lactic acid is a crystalline resin, the impact resistance is also low and is 1 kJ/m2 to 2 kJ/m2 in terms of Izod impact strength, making it difficult to adopt the poly lactic acid in durable members such as electric/electronic equipment products.
In order to overcome the above drawbacks, an attempt has been made to improve physical properties, for example, by adopting a polymer alloy of the biomass-derived resin with a polycarbonate resin that is a petroleum resin. According to this technique, however, the content of the petroleum resin is high and the content of the biomass-derived resin is around 50%, and, consequently, the effect of reducing the amount of fossils used and reducing the amount of carbon dioxide emissions for environmental load reduction purposes such as global warming countermeasure is disadvantageously reduced by half.
For example, PTL 1 proposes an electric/electronic component produced by molding a resin composition containing 1 part by mass to 350 parts by mass, based on 100 parts by mass of a plant-derived resin, of a naturally occurring organic filler, the plant-derived resin being a poly lactic acid resin, the naturally occurring organic filler being at least one filler selected from paper powder and wood powder, 50% by mass or more of the paper powder being accounted for by a used paper powder. The claimed advantage of this proposal is to improve the mechanical strength of the resin by the addition of naturally occurring organic fillers such as paper powder to poly lactic acid. For flame retardancy purposes, however, 23 parts by mass to 29 parts by mass, based on 100 parts by mass of poly lactic acid, of fossil-derived flame retardants such as phosphorus flame retardants should be added. Even when the resin material is changed to biomass materials as a base for environment load reduction purposes, the use of the large amount of fossil-derived flame retardants spoils the effect attained by the use of the biomass materials.
PTL 2 proposes a resin composition containing at least one biodegradable organic polymeric compound, a flame retardant additive containing a phosphorus-containing compound, and at least one hydrolysis inhibitor that inhibits the hydrolysis of the organic polymeric compound. According to this proposal, in order to flame-retard the biodegradable organic polymeric compound such as poly lactic acid, 30 parts by mass to 60 parts by mass, based on 140 parts by mass of the organic polymeric compound, of the flame retardant additive containing the phosphorus-containing compound should be added. Since the flame retardant additive containing the phosphorus-containing compound uses a fossil resource as the starting material, the proportion of biomass is disadvantageously lowered.
Regarding a technique for flame-retarding resin materials using biomass as a starting material, in order to overcome a problem of a high environment load involved in conventional flame retardant materials using petroleum materials, PTL 3 proposes a process for producing an organic-inorganic hybrid flame retardant cellulose material that contains mixing and homogeneously dispersing 0.1 part by mass to 150 parts by mass of an alkoxysilane compound (B) into 100 parts by mass of acetylcellulose (A), then eliminating the acetyl group partially or completely and hydrolyzing and condensing the alkoxysilane compound. According to the proposed method, the acetylcellulose and the alkoxysilane compound are merely kneaded with each other to obtain the organic-inorganic hybrid flame retardant cellulose material. The results of a test of the organic-inorganic hybrid flame retardant cellulose material by a method according to UL94 combustion test show that the combustion time of specimens is increased, but on the other hand, the specimens are completely burned out, indicating that the flame retardancy is unsatisfactory. PTL 3 describes that the material is moldable, but there is no concrete working example on the molding.
In order to accomplish a task of a flame retardant material that is free from the evolution of toxic gases such as dioxin, develops flame retardancy and utilizes a biomass material, PTL 4 proposes a polymeric composition containing a polymeric substance and a flame retardant, the flame retardant containing a polymer having on its side chain a flame retardant compound. Specifically, the flame retardant is a polymer that has on its side chain a heterocyclic compound containing nitrogen as a hetero atom and uses an organism-derived substance such as a nucleic acid base in a part of monomers for the polymer.
The flame retardant material in this proposal contains a polymeric material having on its side chain a flame retardant heterocyclic compound using a hetero atom but is disadvantageous in that the polymeric material as a starting material is not a biomass material and cannot provide a low environment load due to the addition of a large amount. In this conventional technique, the thermoplastic resin is kneaded with the flame retardant. According to this method, the flame retardancy is developed. When molding of the composition for use as a lo molded product is taken into consideration, due to a lowering in affinity between the thermoplastic resin and the flame retardant, disadvantageously, the fluidity of the resin is deteriorated leading to deteriorated moldability and sometimes leading to lowered physical properties.
In order to accomplish a task that simultaneous realization of physical properties such as strength and flame retardancy increases the dependency on petroleum products, PTL 5 proposes a flame retardant polyester resin composition containing 50% by mass to 80% by mass of a naturally occurring biodegradable polyester resin (A) and 50% by mass to 20% by mass of a thermoplastic polyester resin (B) produced by copolymerizing an organophosphorus compound. Specifically, polyethylene terephthalate (PET) or polybutylene succinate (PBS) copolymerized with an organic phosphorus is blended with poly lactic acid.
According to this proposal, however, polyethylene terephthalate produced using a petroleum-derived starting material, and, further, at the present time, succinic acid and butanediol as starting materials for polybutylene succinate are also petroleum-derived starting materials. Accordingly, disadvantageously, there is no difference in degree of biomass between this proposed material and the conventional flame retardant. In this conventional technique, an organophosphorus compound is copolymerized in the structure of the thermoplastic polyester resin. This means that an organophosphorus compound is introduced into a main chain of the thermoplastic polyester resin. Further, due to a feature of the development of flame retardancy by the organophosphorus compound, the flame retardancy is developed by the elimination of phosphorus. Since, however, phosphorus is introduced into the main chain, the elimination is less likely to occur. Even though the elimination successfully occurs, the main chain is cut off, the molecular weight is lowered. Consequently, dripping is likely to occur, and it becomes difficult to ensure flame retardancy. Accordingly, for transfer to lower dependency on petroleum, even when the biomass-derived thermoplastic polyester resin in which the organophosphorus compound is copolymerized is used, the task of simultaneously meeting both the physical properties and the flame retardancy cannot be accomplished.
PTL 6 proposes a flame retardant resin composition containing at least a thermoplastic resin and a flame retardant, the flame retardant being a phosphorus-containing polysaccharide containing a naturally occurring polysaccharide having a phosphoric ester on a side chain thereof. PTL 7 proposes a flame retardant resin composition containing at least a thermoplastic resin and a flame retardant, the flame retardant being a phosphorus-containing polysaccharide containing a naturally occurring polysaccharide having a thiophosphoric ester on a side chain thereof.
Accordingly, any flame retardant resin composition having satisfactory properties that has a low petroleum dependency, a high degree of biomass, a low environment load, and, at the same time, flame to retardancy has not been obtained yet, and, thus, further improvement and development have been demanded in the art.